Impact on soil quality of a 10-year-old short-rotation coppice poplar stand compared with intensive agricultural and uncultivated systems in a Mediterranean area

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Agriculture, Ecosystems and Environment 140 (2011) 245–254

Contents lists available at ScienceDirect

Agriculture, Ecosystems and Environment

journa l homepage: www.e lsev ier .com/ locate /agee

mpact on soil quality of a 10-year-old short-rotation coppice poplar standompared with intensive agricultural and uncultivated systems in aediterranean area

lisa Pellegrinoa,b,∗,1, Claudia Di Benea,1, Cristiano Tozzinia, Enrico Bonaria

Land Lab, Scuola Superiore Sant’Anna, P.za Martiri della Libertà 33, 56127 Pisa, ItalyDepartment of Crop Plant Biology, University of Pisa, Via del Borghetto 80, 56124 Pisa, Italy

r t i c l e i n f o

rticle history:eceived 17 August 2010eceived in revised form 6 December 2010ccepted 8 December 2010vailable online 30 December 2010

eywords:hort-rotation forestry

a b s t r a c t

Bioenergy crops play an ecologically and economically fundamental role as an alternative to agri-foodproductions and as renewable energy sources. Little attention has been focused on soil quality followingconversion of agricultural lands to biomass crops. Here, we assessed the impact of a 10-year-old short-rotation coppice (SRC) poplar stand on the main soil chemical parameters, microbial biomass carbon, soilrespiration, and arbuscular mycorrhizal fungi (AMF), compared with intensive agricultural and unculti-vated systems. Three different harvest frequencies of poplar SRC (annual T1, biannual T2 and triennial T3cutting cycles) were evaluated. Multivariate analysis showed that poplar SRC improved soil quality com-

utting cyclerbuscular mycorrhizal fungiicrobial biomass carbon

oil respirationultivariate analysis

pared with intensive agricultural and uncultivated systems. T1 and T2 positively affected AMF inoculumpotential and root colonisation of a co-occurring plant species, while T3 improved the majority of soilchemical and biochemical parameters. Moreover, three different AMF morphospecies belonging to thegenera Glomus and Scutellospora were found in poplar SRC, while morphospecies belonging exclusivelyto genera Glomus were recorded in intensive agricultural and uncultivated systems. Such aspects haveagro-ecological implications, since the positive changes of soil nutrient availability and carbon content

danc

together with a high abun

. Introduction

During the last 10 years the concept of multifunctional agri-ulture has become established (Van Huylenbroeck and Durand,003). Such multifunctionality includes the conversion into low-

nput cultivation models and non-food productions, and intoractices aiming to protect the rural landscape. In this context,ioenergy crops play an ecologically and economically fundamen-al role as a potential alternative to agri-food production and asenewable energy sources, when they are integrated in an opti-ised and sustainable territorial management of resources (Jordan

t al., 2007). Large emission of greenhouse gases, and in particularf CO2, induced by human activities, promoted a change in energy

oncept and the request for alternative sources, such as biomassrops (Lemus and Lal, 2005). These crops are mainly perennial rhi-omatous grasses or fast-growing trees, such as Eucalyptus, Populusnd Salix (Karp and Shield, 2008; Hinchee et al., 2009).

∗ Corresponding author at: Land Lab, Scuola Superiore Sant’Anna, P.za Martiriella Libertà 33, 56127 Pisa, Italy. Tel.: +39 050 2216650; fax: +39 050 883526.

E-mail addresses: [email protected], [email protected] (E. Pellegrino).1 These authors contributed equally to this work.

167-8809/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.agee.2010.12.011

e and diversity of soil biota show clear soil sustainability of poplar SRC.© 2010 Elsevier B.V. All rights reserved.

Many Populus (poplar) species have high energy potential, pro-duce high yield, reduce soil erosion and are able to grow inmarginal lands and drought conditions, as in Mediterranean areas(Makeschin, 1994; Guidi et al., 2008; Guo et al., 2010). Most speciesused in Europe belong to P. nigra and P. deltoides, although sev-eral hybrids are also successfully cultivated (Hinchee et al., 2009).Many studies have been performed on poplar short-rotation cop-pice (SRC) biomass production and quality, energy balance andmanagement intensity, mainly in relation to fertilisation, irrigation,tillage, crop age and cutting cycles (Kauter et al., 2003; Deckmynet al., 2004; Nassi o Di Nasso et al., 2010). Some of these studieshave compared the benefits of poplar SRC with other bioenergycrops (Bonari et al., 2004; Karp and Shield, 2008), and othershave evaluated the conversion of agricultural lands from food pro-duction to biomass crops, in particular to poplar SRC (Boehmelet al., 2008; Gasol et al., 2010). So far, less attention has beenfocused on the impact of poplar SRC on soil health and qual-ity (Makeschin, 1994; Coleman et al., 2004; Zornoza et al., 2009;

Kahle et al., 2010; Mao and Zeng, 2010), whereas the impact offorestry and of conventional and alternative cropping system man-agements have been largely studied (Carter and Rennie, 1982;Pietikaïnen and Fritze, 1995; Fließbach et al., 2007; Mazzonciniet al., 2010).

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Table 1Mean soil physical and chemical characteristics at the experimental site in 1996 at0–30 cm of depth.

Physical and chemical characteristicsa 1996

Sand [%] 39.4Silt [%] 40.5Clay [%] 20.1P [mg kg−1] 8.8Total N [g kg−1] 1.3SOC [g kg−1] 10.4

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C/N 8.4

a P: available Olsen phosphorus; Total N: Kjeldahl nitrogen; SOC: soil organicarbon; C/N: carbon/nitrogen ratio.

Soil quality has been defined as ‘the capacity of a specific kindf soil to function, within natural or managed ecosystem bound-ries, to sustain plant and animal productivity, maintain or enhanceater and air quality, and support human health and habitation’

Karlen et al., 1997). Soil quality evaluation criteria should meethysical, chemical and biological parameters that are sensitive tohanges in soil conditions (Doran, 2002). The concept of a mini-um data set of indicators was first proposed by Larson and Pierce

1991) and seven key physical and chemical parameters were cho-en as the most adequate. Within such parameters, soil organicarbon (SOC) represents the main chemical indicator, directly influ-ncing aggregation, water retention, nutrient availability, C storend biological diversity (Baldock and Nelson, 2000). Later, Dorannd Parkin (1996) proposed an array of soil physical, chemical andiological characteristics. As regards biological parameters, bio-hemical indicators such as microbial biomass, soil respiration,mic/Corg ratio and metabolic quotient (qCO2) were suggested forheir rapidity of reaction to environmental changes and humanctivities, ease of measurement and reproducibility (Bloem et al.,006; Kutsch et al., 2009). Recently, other studies proposed as bio-

ogical indicators the community diversity and activity of certainaxonomic groups of soil biota (Brussaard et al., 1997). Within soil

icrobes, arbuscular mycorrhizal fungi (AMF) have been showno be responsive soil quality indicators both in crop- and wood-ands (Helgason et al., 1998; Daniell et al., 2001; van der Heijdennd Sanders, 2002; Oehl et al., 2003), although several tree species,ncluding poplar, are exclusively or also colonised by ectomycor-hizal fungi (ECMF) (Lopez-Aguillon and Garbaye, 1990; Rooneyt al., 2009). AMF colonise the roots of most plant species and playkey role on soil fertility and on plant health and fitness (Smith

nd Read, 2008).The aim of this study was to evaluate the impact of a 10-year-

ld short-rotation coppice poplar stand, under different harvestrequencies, on soil quality in comparison with an intensive agri-ultural system and an uncultivated soil. For this purpose, we usedome of the most reliable and sensitive soil chemical and biochem-cal parameters, and with regard to the biological ones, AMF werehosen as indicators.

. Materials and methods

.1. Field experimental site

The field experimental site was located at the “Enrico Avanzi”nterdepartmental Centre for Agro-Environmental Research of theniversity of Pisa (43◦40′N lat; 10◦19′E long, with 1 m above sea

evel and 0% slope), Italy. The soil was a poorly drained allu-

ial loam, classified as Typic Xerofluvent by USDA system (Soilurvey Staff, 1975) and as Fluvisol by FAO (IUSS, 2006). Soil phys-cal and chemical characteristics are shown in Table 1. Climaticonditions were typically Mediterranean: rainfall mainly concen-rated from autumn to spring (mean 948 mm year−1) and mean

nd Environment 140 (2011) 245–254

monthly air temperature ranging from 11 ◦C in February to 30 ◦Cin August (mean of 14.5 ◦C year−1). More details on climate condi-tions are given by Mazzoncini et al. (2008). Before experimentalset-up, the field site was conventionally cultivated with maize(Zea mays L.)–durum wheat (Triticum durum Desf.) rotation (onecrop per year). The cropping system was annually tilled accord-ing to local standard practices: 30–35 cm deep ploughing followedby secondary tillage for seedbed preparation. Fertilisation wasapplied and incorporated into the soil during seedbed prepara-tion for both maize (335 kg ha−1 N, 150 kg ha−1 P and 150 kg ha−1 K)and wheat (175 kg ha−1 N, 90 kg ha−1 P and 135 kg ha−1 K). Chemi-cal pre-emergence and mechanical post-emergence weed controlswere applied during the maize growth, while pre- and post-emergence chemical controls were performed for the wheat.

2.2. Field experimental set-up

A long-term experiment was initiated in winter 1996. Theexperimental field was a completely randomised design withfive management treatments and three replicates (n = 3; plots of500 m2): (1) intensive agricultural system (maize–wheat crop-ping system, MW): plots were still conventionally cultivated withmaize–durum wheat rotation (one crop per year); (2) uncultivatedsystem (US): plots were left to develop under natural successionvegetation, where perennial ryegrass (Lolium perenne L.), roughmeadowgrass (Poa trivialis L.), bermuda grass (Cynodon dactylonL.), orchard grass (Dactylis glomerata L.), and red fescue (Festucarubra L.) mainly grew. No fertiliser or other agricultural practiceswere applied. Forage was annually removed; (3) 1-year cuttingcycle poplar SRC (T1): plots were established using 20 cm longunrooted Populus deltoides Bartr. (Lux clone) cuttings with a densityof 10,000 plants ha−1. The soil was tilled according to the stan-dard practices: deep ploughing as the main tillage in the autumn,and disk and rotary harrowing before planting. Chemical weedcontrol was performed before planting by applying 2.5 kg ha−1

of glyphosate and NPK fertilisation was incorporated into thesoil (48 kg ha−1 N, 144 kg ha−1 P and 144 kg ha−1 K). T1 plots wereharvested every year at the end of February, before vegetativere-growth; (4) 2-year cutting cycle poplar SRC (T2): plots were cul-tivated and managed as T1, except for the harvesting frequencywhich was set every 2 years according to the rotation; (5) 3-yearcutting cycle poplar SRC (T3): plots were cultivated and managedas T1 and T2, except for the harvesting cycle of 3 years.

2.3. Sampling

In April 2005, during wheat growth in MW plots, one com-bined soil sample, resulting from three random soil cores pooledtogether, was collected from each replicate plot (0–10 cm depth)in order to control physical and chemical soil spatial variabilitywhich has been shown also to affect at different scales severalAMF proprieties (Hart and Klironomos, 2002; Wolfe et al., 2007;Mummey and Rillig, 2008). With regard to temporal variability ofthe soil quality parameters, in several climatic conditions, includingour areas, chemical characteristics slightly change during the year,while biochemical and biological parameters, including AMF, havebeen shown to consistently maintain the same patterns of vari-ability among systems differently managed although they changedwith the season (Helgason et al., 1999; Vandenkoornhuyse et al.,2002; Di Bene, 2003; Oehl et al., 2003; Stukenbrock and Rosendahl,2004; Bastida et al., 2006; Pellegrino, 2007; Pellegrino et al., 2010).

In addition, after long-term changes, in the evaluation of stablesystems it is important to avoid sampling close to soil treatmentssuch as tillage, fertilisation, weed control and harvest (Picci andNannipieri, 2002). Therefore, we sampled only once in April sinceearly spring sampling was the best choice with respect to the above

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E. Pellegrino et al. / Agriculture, Ecosys

dvice. Actually, all the management operations were concentratedn autumn–winter (tillage, fertilisation and weed control) and latepring–summer (cutting and harvest). Moreover, such a samplingeriod is also considered the best time to assess microbiologicalarameters since soil characteristics are relatively stable, the land

s dry enough to access, all the plants are actively growing and thedentification of AMF spores is easier than in autumn due to theewer amounts of young and immature spores (Oehl et al., 2003;loem et al., 2006). We take all these facts as a strong justification

or choosing early spring as single sampling date.Soil samples used for the chemical analyses and for the assess-

ent of the mycorrhizal infection potential were oven dried at0 ◦C and passed through a 2 mm sieve, whereas samples usedor biochemical analyses were sieved at field moisture. L. perenneas identified as a common and co-occurring plant species. Soil

nd roots of such plant were sampled by extracting turfs (n = 3),pproximately 7–10 cm across and 10 cm deep, from all the plots.n addition, turfs across the main crops, durum wheat and poplar,

ere sampled from the plots under the MW and SRC treatments.fter transport to the laboratory, each turf was carefully washed inater taking care to avoid breaking the roots. Only the fine roots

ttached to the main roots of the target plants (L. perenne, T. durumnd P. deltoides) were collected and stored in a cool dry place prioro assessment of the AMF root colonisation.

.4. Soil chemical and biochemical analyses

Soil samples were analysed for: pH; cation exchange capac-ty, CEC; electrical conductivity, EC; available phosphorus, P; totalitrogen, total N; organic carbon, SOC; microbial biomass carbon,BC and soil respiration, SR. All such analyses were carried out in

hree replicates in order to control the variability. Soil pH and ECere measured in deionised water (1:2.5 and 1:2, w/v, respectively)

McLean, 1982) and CEC was evaluated by the Rhoades method1982). P was determined by colorimetry using the Olsen methodOlsen and Sommers, 1982). Total N was evaluated by macro Kjel-ahl digestion procedure (Bremner and Mulvaney, 1982) and SOCsing the modified Walkley–Black wet combustion method (Nelsonnd Sommers, 1982). MBC and SR were assessed on soil samplesdjusted to 55% of the field capacity on the basis of the ideal waterontent for an evaluation of microbial activity. MBC was deter-ined by the Vance chloroform fumigation-extraction method,hile SR was estimated according to the Isermeyer method,escribed in Alef and Nannipieri (1995). Such biochemical param-ters were assessed using titration on soil subsamples of 45 g after0 days of incubation in closed jars maintained at 25 ◦C.

Soil C/N ratio was calculated dividing SOC by organic N.mic/Corg and Cmic/SR (metabolic quotient, qCO2) ratios were cal-ulated dividing MBC by SOC and SR, respectively, and utilised asndices of microbial biomass contribution to soil organic carbon andespiration (Anderson and Domsch, 1989).

.5. AMF measurements

The percentage of AMF colonisation was assessed after clear-ng and staining with lactic acid instead of phenol (Phillips andayman, 1970), using the gridline intersect method (Giovannettind Mosse, 1980).

Mycorrhizal infection potential of soil was evaluated by a rapidest to assess AMF infectivity (mycorrhizal infection potential,

IP). Lettuce (Lactuca sativa L.) seeds were sown in 50 mL ster-

lised plastic tubes filled with 40 mL of soil obtained by each plotnd six replicate tubes were used. After emergence, the lettucelants were thinned to three. The plants were removed from theubes after 2 weeks’ growth and the root systems were staineds described above, mounted on microscope slides and examined

nd Environment 140 (2011) 245–254 247

under a Reichert-Jung (Vienna, Austria) Polyvar light microscope.Root length and colonised root length were measured using a grideyepiece. Number of infection units, measured as hyphae withentry points, and number of entry points were assessed at a mag-nification of 125–500× and verified at a magnification of 1250×.

AMF spores were assessed in 50 g of soil per each plotby wet sieving and decanting, followed by sucrose centrifu-gation (Sieverding, 1991). After centrifugation, the supernatantwas sieved by 50 �m mesh and quickly rinsed with tap water.Spore number was counted using a Petri dish under a dis-secting microscope and presented as spore density (numberof spores per gram of soil). AMF spores, spore clusters andsporocarps were separated on the basis of size and colour,and then mounted on microscope slides using polyvinyl–lacticacid–glycerol (PVLG) or PVLG mixed 1:1 (v/v) with Melzer’sreagent. The slides were examined under a Reichert-Jung (Vienna,Austria) Polyvar light microscope and morphospecies were iden-tified following current species descriptions and identificationmanuals (Schenck and Pérez, 1990; International Culture Collec-tion of Vesicular and Vesicular-Arbuscular Endomycorrhizal Fungi[http://invam.caf.wvu.edu/Myc Info/Taxonomy/species.htm]). Atleast 50 spores of each morphospecies were observed and mea-sured using a grid eyepiece. Relative abundance of the identifiedAMF morphospecies was calculated by dividing the number ofspores belonging to each species by the total number of spores (atleast 100 randomly selected spores per each plot). Shannon’s index(H0), as an additional measure of AMF diversity, was calculated bythe formula: H0 = −

∑pi ln pi (pi is the relative abundance of the ith

species compared with all species identified in a sample).

2.6. Statistical analyses

Data were analysed by one-way analysis of variance (ANOVA),using management as the factor. Data were ln- or arcsine trans-formed when needed to fulfil the assumptions of ANOVA, whichwas carried out according to the completely randomised design.Tukey-B procedure was used for comparing means. H0 data showedneither a normal distribution of error terms nor constant errorvariance, therefore a non-parametric ANOVA was required. Weused the Kruskal–Wallis test and then Mann–Whitney U-test aspost-hoc. Means and standard errors given in the tables are foruntransformed data. Linear regression analysis was used to testwhether there was a correlation between number of entry pointsand AMF colonised root length. All the analyses were performed onSPSS 17.0 software (SPSS Inc., Chicago, IL, USA).

All parameters utilised to evaluate soil quality and AMFmorphospecies data were separately evaluated in constrained ordi-nation analyses (redundancy analysis, RDA), in order to investigatethe influence of different managements (used as explanatory vari-ables) either on soil quality parameters or the AMF morphospeciesstructure (used as response variables). A detrended canonical cor-respondence analysis (DCCA) for AMF morphospecies structuresuggested the use of linear method, as the lengths of gradientswere < 3. RDAs were conducted in Canoco for Windows version4.5 (ter Braak and Smilauer, 2002). Additionally, Monte–Carlo per-mutation tests were conducted using 499 random permutationsin order to determine the statistical significance of the relationbetween the different managements and the two data matrixes.

3. Results

3.1. Chemical parameters

After 10 years of different land use, in the 0–10 cm soil depth,CEC, EC and C/N did not show any significant impact of manage-

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248 E. Pellegrino et al. / Agriculture, Ecosystems and Environment 140 (2011) 245–254

Table 2Soil chemical parameters measured in poplar SRC, intensive agricultural and uncultivated systems 10 years after experimental set-up (0–10 cm depth).

Chemical parametersa Poplar SRCb MW US

T1c T2 T3

pH (H2O, 1:2.5)* 8.19 ± 0.01d bc 8.11 ± 0.01 ab 8.06 ± 0.01 a 8.19 ± 0.05 bc 8.23 ± 0.03 cCEC [cmol kg−1] 10.23 ± 0.18 9.63 ± 0.84 11.58 ± 0.47 7.64 ± 0.42 12.98 ± 4.01EC [�S cm−1] 92.00 ± 3.46 113.33 ± 7.22 100.00 ± 2.31 101.00 ± 5.20 103.67 ± 6.06P [mg kg−1]** 12.05 ± 0.40 a 12.24 ± 0.79 a 15.93 ± 0.52 b 9.33 ± 0.10 a 12.25 ± 1.61 aTotal N [g kg−1]*** 1.44 ± 0.03 b 1.37 ± 0.07 b 1.65 ± 0.00 c 1.16 ± 0.03 a 1.34 ± 0.07 abSOC [g kg−1]** 12.37 ± 0.20 ab 13.50 ± 1.10 bc 16.07 ± 0.66 c 10.03 ± 0.54 a 12.07 ± 0.92 abC/N 8.95 ± 0.06 10.23 ± 0.33 10.13 ± 0.43 8.98 ± 0.39 9.33 ± 0.27

a CEC: cation exchange capacity; EC: electrical conductivity; P: available phosphorus; Total N: Kjeldahl nitrogen; SOC: soil organic carbon; C/N: carbon/nitrogen ratio.b Poplar SRC: poplar short-rotation coppice; MW: intensive agricultural system, based on maize–wheat crop rotation; US: uncultivated system.

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*P < 0.05; **P < 0.01; ***P < 0.001).

ent, whereas pH, P, total N and SOC were significantly affectedy the treatments (Table 2). Soil pH value was significantly higher

n US than in T3, while the amount of P, ranging from 9.33 to5.93 mg kg−1 in MW and T3, respectively, produced two differentroups with high and low P concentration: T3 and other treatmentsTable 2). Total N was significantly higher in poplar SRC than in

W, while T2 and T3 significantly increased SOC compared withW (Table 2).

.2. Biochemical parameters

Microbial biomass carbon (MBC) and soil respiration (SR) wereignificantly affected by the management (Table 3). In contrast,mic/Corg ratio did not differ among the treatments (Table 3). MWnd T3 showed the lowest and the highest values of both MBC andR (Table 3). In detail, MBC ranged from 91.20 and 148.35 mg C kg−1

oil, while SR ranged from 60.72 to 163.27 mg CO2-C kg−1 soilTable 3). In MW and in US, MBC was significantly lower than inoplar SRC (Table 3). Among poplar SRC, three different groupsere observed: T1 (low MBC), T2 (medium MBC), and T3 (highBC) (Table 3). Similarly to MBC, SR in MW was significantly

ower than in poplar SRC and US (Table 3). In detail, two differ-nt groups can be distinguished: T1 (low SR) and T3 (high SR)Table 3).

The Cmic/Corg ratio did not significantly differ among thereatments, ranging from 0.89% to 1.79% in T1 and the US, respec-ively (Table 3). On the other hand, the mineralised C per unit of

icrobial biomass C (qCO2) was significantly influenced by theanagement, showing values ranging from 0.66 to 1.35 mg CO2-mg Cmic−1 d−1 in MW and US, respectively (Table 3). As regard

o poplar SRC, qCO2 increased from T3 to T1, which showed val-es significantly different between each other and similar to T2Table 3).

able 3oil biochemical parameters measured in poplar SRC, uncultivated soil and maize–wheat

MBCmg C kg−1 soil

SRa

mg CO2-C kg−

Poplar SRCb

T1c 109.97 ± 0.17d b 140.30 ± 0.9T2 135.32 ± 0.49 c 153.79 ± 6.8T3 148.35 ± 1.01 d 163.27 ± 2.4

Uncultivated soil 94.46 ± 1.95 a 127.75 ± 4.3MW cropping system 91.20 ± 2.90 a 60.72 ± 4.4

a MBC: microbial biomass carbon; SR: soil respiration; Cmic/Corg: microbial carbon/sob Poplar SRC: poplar short-rotation coppice; MW cropping system: maize–wheat croppc T1: 1-year cutting cycle; T2: 2-year cutting cycle; T3: 3-year cutting cycle.d Values are means ± SE of three plots for each treatment. Values in each column not fo

P < 0.001).

owed by the same letters are significantly different as tested by one-way ANOVA

3.3. AMF measurements

3.3.1. Mycorrhizal colonisationThe percentage of colonised root length of P. deltoides was not

significantly affected by the cutting cycle (P = 0.09), ranging from15.3% to 18.7% (in T2 and T3, respectively). L. perenne in US andT. durum in MW showed mycorrhizal colonisation values of 3.8%and 8.8%, respectively. All poplar samples, carefully analysed alongthe fine root tips, did not show any outer sheath-like structurescharacteristic of the ECMF.

In all replicate plots of poplar SRC, of US and of MW, L. perennewas consistently detected. Mycorrhizal colonisation of such com-mon and co-occurring plant species weed was significantly affectedby management (Table 4). The highest mycorrhizal colonisation ofL. perenne was observed in T2, and such value significantly dif-fered from those recorded in T1 and T3 (Table 4). In addition, L.perenne grown in MW and US was significantly less colonised byAMF, showing values ranging from 5.9% to 9.4% (Table 4).

3.3.2. Mycorrhizal infection potentialMycorrhizal infection potential (MIP) was assessed using three

different parameters: colonised root length, number of infectionunits and number of entry points of L. sativa roots. Colonised rootlength showed values ranging from 0.41% to 3.68% in US and T2,respectively (Table 5). The differently managed poplar SRC showedcolonised root lengths significantly different from each other, andhigher than those reported in US and MW (Table 5). Infection unitsvalues ranged from 0.13 to 3.18 units cm−1 root length in MW and

T2, respectively, while the number of entry points from 0.11 to3.28 cm−1 root length in US and T2, respectively (Table 5). Amongthe managements, three different groups with low, medium andhigh infectivity can be discriminated using the infection unitparameters: MW and US (low infectivity), T3 (medium infectivity),

cropping system 10 years after experimental set-up (0–10 cm depth).

1 soilCmic/Corg (%) qCO2

mg CO2-C mg Cmic−1 d−1

0 bc 0.89 ± 0.02 1.28 ± 0.01 cd2 cd 1.02 ± 0.08 1.14 ± 0.05 bc7 d 0.93 ± 0.03 1.10 ± 0.01 b2 b 1.79 ± 0.07 1.35 ± 0.06 d0 a 0.91 ± 0.03 0.66 ± 0.04 a

il organic carbon ratio; qCO2: metabolic quotient, SR/MBC.ing system.

llowed by the same letters are significantly different as tested by one-way ANOVA

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E. Pellegrino et al. / Agriculture, Ecosystems and Environment 140 (2011) 245–254 249

Table 4Mycorrhizal colonisation of Lolium perenne, spore density and arbuscular myc-orrhizal fungal morphotype diversity estimated using Shannon’s measure (H0)revealed in poplar SRC, uncultivated soil and maize–wheat cropping system 10 yearsafter experimental set-up (0–10 cm depth).

Mycorrhizalcolonisation(%)

Number of sporesg−1 soil

H0

Poplar SRCa

T1b 16.90 ± 0.23c c 11.70 ± 0.46 b 0.97 ± 0.00 dT2 18.90 ± 0.13 d 12.40 ± 0.17 b 1.01 ± 0.03 dT3 17.35 ± 0.32 c 16.90 ± 1.93 c 0.68 ± 0.00 b

Uncultivated soil 5.93 ± 0.12 a 4.63 ± 0.19 a 0.79 ± 0.00 cMW cropping system 9.37 ± 0.55 b 5.68 ± 0.32 a 0.42 ± 0.01 a

a Poplar SRC: poplar short-rotation coppice.b T1: 1-year cutting cycle; T2: 2-year cutting cycle; T3: 3-year cutting cycle; MW

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Fig. 1. Relative spore abundance in 1-, 2- and 3-year cutting cycle (T1, T2 and T3)poplar short-rotation coppice; intensive agricultural system: maize–wheat crop-

ropping system: maize–wheat cropping system.c Values are means ± SE of three plots for each treatment. Values in each column

ot followed by the same letters are significantly different as tested by one-wayNOVA (P < 0.001) and by the Kruskall–Wallis non-parametric test (P = 0.012).

nd T1 and T2 (high infectivity) (Table 5). Using the numberf entry points a similar trend was observed: MW and US (lownfectivity), T3 (medium infectivity), T1 (medium–high infectivity),nd T2 (high infectivity) (Table 5). The number of entry points andolonised root length were positively correlated with each otherR2 = 0.62, P = 0.001).

.3.3. AMF spore populationThe spore density significantly differed among managements,

anging from 4.6 to 16.9 spore g−1 of soil in US and T3, respec-ively (Table 4). US and MW showed a similar spore density, whichas significantly lower than that reported in poplar SRC (Table 4).lthough no differences were observed between T1 and T2, suchanagements significantly reduced the spore density comparedith T3 (Table 4).

Overall, on the basis of spore morphology, we detected six differ-nt AMF species belonging to the genera Glomus and Scutellospora:lomus etunicatum (Beck. & Gerd.), Glomus geosporum (Nicol.Gerd.), Glomus intraradices (Schen. & Smith), Glomus mosseae

Nicol. & Gerd.), Scutellospora calospora (Nicol. & Gerd.) and annidentified Glomus species (Fig. 1). In T1 and T2 three AMF speciesere recorded (G. mosseae, Glomus sp. and S. calospora), while in

3 only two species were observed (G. mosseae and S. calospora)

Fig. 1). In US and in MW four (G. etunicatum, G. geosporum, G.ntraradices and G. mosseae) and three AMF species (G. geosporum,. intraradices and G. mosseae) were detected, respectively (Fig. 1).he AMF community of soil under different managements were

able 5olonised root length, number of infection units and number of entry points ofactuca sativa grown in poplar SRC, uncultivated soil and maize–wheat croppingystem 10 years after experimental set-up (0–10 cm depth).

Colonised rootlength (%)

Infection unitscm−1 rootlength

Entry pointscm−1 rootlength

Poplar SRCa

T1b 1.63 ± 0.07c b 2.46 ± 0.09 c 2.43 ± 0.09 cT2 3.68 ± 0.31 d 3.18 ± 0.52 c 3.28 ± 0.42 dT3 2.30 ± 0.04 c 1.35 ± 1.12 b 1.32 ± 0.08 b

Uncultivated soil 0.41 ± 0.12 a 0.13 ± 0.02 a 0.11 ± 0.03 aMW cropping system 0.63 ± 0.17 a 0.13 ± 0.03 a 0.13 ± 0.02 a

a Poplar SRC: poplar short-rotation coppice; MW cropping system: maize–wheatropping system.

b T1: 1-year cutting cycle; T2: 2-year cutting cycle; T3: 3-year cutting cycle.c Values are means ± SE of three plots for each treatment. Values in each column

ot followed by the same letters are significantly different as tested by one-wayNOVA (P < 0.001).

ping system, MW; uncultivated system: US. The values are means of three replicatesper treatment. Each colour corresponds to an AMF species: Glomus geosporum, Glo-mus etunicatum, Glomus intraradices, Glomus sp., Glomus mosseae and Scutellosporacalospora.

determined on the basis of the relative spore abundances of the sixAMF species (Fig. 1). The most common species in poplar SRC wereS. calospora and G. mosseae. S. calospora ranged from 43% to 58% inT2 and T3, respectively, while G. mosseae from 40% to 42% in T2 andT1–T3, respectively (Fig. 1). In US, the most abundant species wereG. geosporum and G. mosseae (28% and 34%, respectively), while inMW were G. geosporum and G. intraradices (46% and 51%, respec-tively) (Fig. 1). H0, ranging from 0.42 to 1.01 in MW and T2, wassignificantly affected by the management (P = 0.012), as shown bythe Kruskall–Wallis test (Table 4). According to our initial hypothe-sis, the AMF diversity was lowest in MW, but unexpectedly T1 andT2 showed higher diversity (H0 ≥ 0.97) than US (H0 = 0.79) (Table 4).

RDA showed that management explained 88.1% (I and II axes) ofthe whole variance and that its effect on AMF communities was sig-nificant (P = 0.004) (Fig. 2a). In detail, the Monte–Carlo permutationtest showed that all treatments were significantly different amongeach other (P ≤ 0.004). In the biplot of the RDA (Fig. 2a) the centroidsof MW and US are distanced from each other and from poplar SRC,while the centroids representing the differently managed poplarSRC cluster, share S. calospora and G. mosseae. The biplot also showsthat T1 and T2 centroides are closer to each other than to T3, sharingGlomus sp. (Fig. 2a). In addition, the arrow representing G. etunica-tum points to US and the arrow representing G. intraradices andG. geosporum point to MW, showing their preferential presence insuch managements (Fig. 2a).

3.4. Main patterns of chemical, biochemical and AMF as affectedby agroecosystem management

RDA showed that management explained 59.6% (I and II axes)of the whole variance and that its effect on the whole soil qual-ity parameters was significant (P = 0.002) (Fig. 2b). In detail, theMonte–Carlo permutation test showed that all treatments weresignificantly different to each other (P ≤ 0.004). In the biplot of theRDA (Fig. 2b), the centroids of MW and US are distant from eachother and from poplar SRC. The centroids representing the differ-ently managed poplar SRC are also distant from each other (Fig. 2b).Soil quality parameter arrows point to poplar SRC, clearly showingtheir higher values compared with US and MW (Fig. 2b). In addition,the arrows show that values of mycorrhizal infection potential are

higher in T1 and T2 than in T3, while the values of MBC, SR, SOC, P,total N and CEC are highest in T3 (Fig. 2b). The diagram points outcorrelations between mycorrhizal infection potential parameters,between SOC and SR, and between P and total N (Fig. 2b). The biplotalso shows that AMF spore density and MBC represent the most

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Fig. 2. Redundancy analysis (RDA) biplot based on: (a) arbuscular mycorrhizal fun-gal (AMF) spore number per gram of soil (Scutellospora calospora, Glomus mosseae,Glomus sp., Glomus intraradices, Glomus etunicatum and Glomus geosporum); (b)chemical, biochemical and AMF parameters (pH; CEC: cation exchange capacity;EC: electrical conductivity; P: available Olsen phosphorus; total N: Kjeldahl nitro-gen; SOC: soil organic carbon; SR: soil respiration; MBC: microbial biomass carbon;mycorrhizal colonisation of Lolium perenne: RC; spore density: SD; number of entrypoints: NEP; number of infection units: IU) and treatments (1-, 2- and 3-year cuttingcycle poplar short-rotation coppice: T1, T2 and T3, respectively; intensive agri-cultural system: maize–wheat cropping system, MW; uncultivated system: US).Treatments are represented by down-triangle (T1), square (T2), star (T3), cross (US)and circle (MW). The AMF morphospecies in (a) and the chemical, biochemical andAfce

dw

4

1pmit(iuqd

4

t(c

MF parameters in (b) are represented by arrows. (a) The 1st and 2nd axis accountedor 72.2 and 88.1 of the variability explained by all canonical axes and were signifi-ant (P = 0.002); (b) the 1st and 2nd axis accounted for 50.3 and 59.6 of the variabilityxplained by all canonical axes and were significant (P = 0.002).

iscriminating variables between US and MW vs. SRC treatments,hile CEC, total N and P between T1 and T2 vs. T3 (Fig. 2b).

. Discussion

In this work, for the first time, we assessed the impact of a0-year-old bioenergy crop management based on a SRC poplarlantation on soil quality, using the main chemical parameters,icrobial biomass, soil respiration and AMF root colonisation,

nfectivity, spore density, community composition and struc-ure, compared with intensive agricultural (MW) and uncultivatedUS) systems. Multivariate analyses showed that: (i) poplar SRCmproved soil quality compared with MW and US; (ii) poplar SRCnder the three harvest frequencies differentially increased soiluality: T1 and T2 affected AMF positively, except for spore pro-uction, while T3 improved chemical and biochemical parameters.

.1. Chemical parameters

With the conversion from maize–wheat cropping system (MW)o poplar SRC and uncultivated system (US), only 2- (T2) and 3-yearT3) cutting cycle poplar SRC topsoil layer revealed higher SOC con-entration compared with the plots maintained under MW, which

nd Environment 140 (2011) 245–254

had SOC level similar to the initial value. A recent meta-analysis,evaluating several tree species in different stand age afforestationprogrammes of agricultural soils, reported SOC increases rangingbetween 2% and 25% due to coniferous and broadleaf plantations(Laganière et al., 2010). With regard to poplar, Hansen (1993) andColeman et al. (2004) found a mean annual carbon (C) increase ofabout 1.60 and 3 Mg ha−1. Our data are consistent with the find-ings of several authors, who in general reported long-term positiveSOC changes due to poplar afforestation of former cultivated lands(Hansen, 1993; Makeschin, 1994; Coleman et al., 2004). On the con-trary, a meta-analysis on soil property changes due to afforestationby different tree genera showed contrasting results, since Pinusreduced SOC content by 15%, whereas some other conifers andEucalyptus did not significantly increase SOC levels (Berthrong et al.,2009a). Moreover, recent studies on Populus reported no significantchanges in 0–15 cm layer in the first 15 years following afforesta-tion of agricultural soils (Mao and Zeng, 2010). Such contradictoryreports may be due to variables controlling SOC dynamics, suchas previous land use, time since land-use conversion, tree speciesplanted, soil clay content, pre-planting disturbance and climaticconditions (Laganière et al., 2010).

Here, as observed in most studies, soil nutrient concentrationsand pH were strictly related to SOC patterns (Paustian et al., 1997;Lemus and Lal, 2005). All SRC poplar treatments had higher soiltotal N compared with MW, while soil P concentration significantlyincreased only under T3, which showed the lowest pH value. T3increased total N by 42% compared with MW, while T1 and T2increased such value by a mean of 22%. Accordingly, in severalafforestations, including poplar plantations, stand age was reportedto increase soil N content (Ritter, 2007; Sartori et al., 2007; Mao andZeng, 2010). In particular, 10-, 12- and 20-year poplar afforesta-tions increased soil total N by 40%, 20% and 23% compared withagricultural lands (Kahle et al., 2007; Sartori et al., 2007; Mao andZeng, 2010). By contrast, Berthrong et al. (2009a) showed a nega-tive change of soil N, similarly to SOC trend, in Pinus afforestationand no changes in Eucalyptus and other tree genera. Moreover, soilN decreases were revealed in Eucalyptus and Pinus by other authors(Binkley and Resh, 1999; Smal and Olszewska, 2008). In our study, Nincrease in SRC poplar soils, compared with other treatments, maybe due to less soil disturbance, high plant litter quantity and inten-sive and deep rooting, decreasing percolation water with nutrientsand especially soil N losses. Inconsistent results concerning soil Nchanges may be a consequence of tree species planted, soil typeand management (Sartori et al., 2007; Berthrong et al., 2009a).

Soil P content is known to be the one of the major growth-limiting elements, because P is often bound in insoluble formsor is physically retained by aggregates (Ritter, 2007). Here, T3increased soil available P, by 30%, 31% and 71% in comparison withUS, other poplar SRC and MW, respectively. Interestingly, Zornozaet al. (2009) comparing soil available P in Pinus forest, agriculturaland uncultivated soils in a Mediterranean area, observed increasesof 41% and 91% under forest management compared with the otherland uses. Moreover, as regards total P, which is correlated with theavailable P, Ritter (2007) reported soil increases of 3% and 15% fol-lowing afforestation with Larix and Betula compared with grazed,treeless areas.

In T3 plots we observed a decrease of 0.13 pH units comparedwith MW. Berthrong et al. (2009a) reported that plantations withEucalyptus, Pinus and other conifers decreased soil pH of 0.30 units.Although such changes are similar to our data, they observed vari-ation of pH from 5.6 to 5.3, due to the fact that the control soil was

already acidic. In Populus and Salix, a minor decrease in soil pH wasfound even 3 years after tree plantation and in Populus stands alsoalong with length of rotation (Makeschin, 1994; Sartori et al., 2007).On the contrary, Kahle et al. (2007, 2010) did not observe any soilpH change due to poplar plantation.

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E. Pellegrino et al. / Agriculture, Ecosys

.2. Biochemical parameters

In the present study, all poplar SRC treatments increased MBCnd SR by a mean of 44% and 151%, respectively, compared withhe maize–wheat cropping system, while the uncultivated systemhowed MBC and SR increases of 4% and 110%, respectively, in com-arison with MW. Our results are consistent with previous workstudying MBC or SR changes under forestry management comparedith agricultural lands, supporting the hypothesis that soil MBC

ncreases following afforestation of agricultural lands (Makeschin,994; Zornoza et al., 2009; Kahle et al., 2010; Mao and Zeng, 2010).nly a few studies have evaluated SRC poplar impact on microbialiomass and activity assessed on the basis of SR. Makeschin (1994),omparing the effect of energy forestry and of an intensive wheatropping system on biochemical parameters, reported increases ofBC 9 years after land use change. Consistently, Kahle et al. (2010),

tudying the impact of afforestation of agricultural lands on micro-ial proprieties, observed positive MBC changes. As regards MBChifts, Mao and Zeng (2010) reported an initial decline and then aignificant increase with stand age. In contrast with our findings,everal authors have shown that forest management determines aecline in soil MBC ranging from −27% to −43% (Pietikaïnen andritze, 1995; Chen et al., 2003; Berthrong et al., 2009b).

Increases in soil MBC due to poplar afforestation was notnexpected because of higher energy and nutrient sources forecomposer microorganisms, supplied by a larger quantity of leafnd root litter in comparison with crop residues. Moreover, soilBC increases may depend also on no-tillage practices during the

lantation period and on high plant coverage (Gupta et al., 1994).oncerning such factors, it is well established that ploughing neg-tively affects MBC by reducing SOC content in the shallow layerCarter and Rennie, 1982).

The similarity of Cmic/Corg ratio among the different man-gements might show that soil microorganisms have a similaretabolic behaviour in all treatments and a similar efficiency in the

onversion of organic C into microbial biomass C, in agreement withhe concentrations of the soil organic carbon, which were similarn all the plots, except for the T3 (Bastida et al., 2006; Zornoza et al.,009; Frazão et al., 2010). The Cmic/Corg values in the SRC poplarnder different cutting cycles were 53% and 62% lower than thateported under Pinus and Populus plantations, respectively (Bastidat al., 2006; Zornoza et al., 2009; Mao and Zeng, 2010). In the MWnd US systems, the values of this index were comparable to thatbserved by Frazão et al. (2010) in similar systems, although lowerhan those reported by Zornoza et al. (2009) and by Fließbach et al.2007). Moreover, in conventional and organic systems adjacento our field sites, Cmic/Corg values lower than that observed hereere found (Mazzoncini et al., 2010).

The metabolic quotient (qCO2) is an index that estimates thectivity and efficiency of decomposition by soil microorganismsy evaluating the CO2 loss through respiration: low respirationer unit of microbes represents high efficiency (Anderson andomsch, 1990; Kutsch et al., 2009). Here, the MW system showedlower qCO2 than poplar SRC treatments. Litter inputs in Populuslantations, which represent the substrate for respiration, couldetermine the increase of this index as suggested also by Bastidat al. (2006). Moreover, the differences between MW and US mighte due to changes in species composition within microbial commu-ities which is largely reported to be highly related to changes inlant diversity (Smalla et al., 2001; Johnson et al., 2003; Öpik et al.,006). Actually, the AMF species richness in US was twofold than

hat observed in MW.

The limitation of a single sampling date is that biochemicalarameters can vary through the season due to the effects of factorsuch as temperature, moisture, photosynthate production and/orheir interactions (Luo and Zhou, 2006; Kutsch et al., 2009). The

nd Environment 140 (2011) 245–254 251

consequence is that we cannot assume that the values observedin the different treatments will remain constant through the year.In fact, in adjacent conventionally tilled and no-tilled plots, val-ues of MBC and SR higher and similar than that obtained here inthe intensive agricultural and uncultivated systems were observedin autumn and spring, respectively (Di Bene, 2003). Nevertheless,this does not invalidate our data on the impacts of managementon biochemical parameters since several authors observed variablevalues of MBC, SR, Cmic/Corg and qCO2 through the season but con-sistent differences among treatments (Di Bene, 2003; Bastida et al.,2006; Frazão et al., 2010).

4.3. AMF measurements

L. perenne has a fibrous root system, with thick main roots andthinner lateral branches, which are usually colonised by AMF. Sucha common and co-occurring plant species was chosen as a suitabletest plant, due to its well known responsiveness to a wide rangeof AMF and soil conditions (Oehl et al., 2003; Gollotte et al., 2004).Here, we observed that L. perenne, growing in SRC poplar plots,showed an AMF colonisation 1–2 times higher than the colonisationof the same plant species occurring in the maize–wheat (MW) rota-tion and in the uncultivated system (US). The differences betweenSRC and MW L. perenne colonisation rate can be well explainedmainly by ploughing, fertilisation or fungicide application, whilethose between SRC and US by root system architecture and devel-opment of the plant species growing in the different treatments. Asto AMF root colonisation, several authors have shown that plough-ing and disturbance reduce the extent and interconnectedness ofAMF extraradical mycelium spreading from mycorrhizal roots intothe surrounding soil (McGonigle and Miller, 1996; Helgason et al.,1998) and, in some cases, disturbance was also shown to negativelyaffect root colonisation rates (Koske and Gemma, 1997). Moreover,the production and mortality dynamics of fine roots, which are anessential component of the poplar root system (Block et al., 2006),might determine a greater AMF colonisation of L. perenne in poplarSRC compared with US, where only herbaceous species were grow-ing.

Two main methods have been developed in order to evaluateAMF inoculum potential by means of infective propagule or sporenumber (Porter, 1979). In our study, infective propagule number,measured using lettuce AMF colonisation, infection units, numberof entry points and AMF spore richness were consistently higherin poplar SRC than in MW and US. Changes of AMF abundance andinfectivity due to disturbance, fertilisation or pesticide applications,plant community composition, have been previously shown in sev-eral studies (Bever et al., 1996; Oehl et al., 2003, 2004). In particular,Baum and Makeschin (2000) and Chifflot et al. (2009) studying AMFformation under poplar plantation, observed an AMF spore densityconsistent with our data.

Ten years after starting the long-term field experiment, the AMFspore density revealed under MW and US showed values lower thanunder SRC. The values observed under MW are consistent with thedata reported in conventionally or organically agricultural fieldsbelonging to the same area and with those found in microcosmsusing soil originating from arable lands under a similar crop rota-tion (Oehl et al., 2004; Pellegrino, 2007; Mazzoncini et al., 2010).Nevertheless, MW and US spore density were lower than in arablelands and grassland in UK and Central Europe (Eason et al., 1999;Oehl et al., 2003).

Intensive harvesting and herbivory were shown to reduce C

accumulation rates below-ground, as a result of above-groundplant re-growth (Barto and Rillig, 2010). Such C decreases mayexplain the reduction of AMF spore occurrence in T1 and T2 com-pared with T3 due to the fact that AMF are dependent on plants fortheir C nutrition. So far, we have no information about C allocation

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52 E. Pellegrino et al. / Agriculture, Ecosys

o fungal component following coppicing. Concerning C allocation,ooney et al. (2009) suggested that coppicing initially determinesplant retain aiming at tree regeneration. According to their sug-estions, Nassi o Di Nasso et al. (2010) observed dry yield and stemiameter increases of 38% and 73%, respectively, under the 3-yearutting cycle poplar SRC in comparison with T1 and T2.

Our data showed that significant AMF spore population changes,ue to poplar SRC management, occurred 10 years after poplarlantation. Three different AMF morphospecies belonging to theenera Glomus and Scutellospora were found in SRC poplar plots,hile three and four morphospecies belonging to the genera Glo-us were recorded in MW and US, respectively.

This finding may reflect the edaphic and climatic homogeneityf the studied area. Similar spore richness were observed in arableoils and tree plantations (Del Val et al., 1999; Calvente et al., 2004),hile higher values were reported in adjacent fields subjected to

onventional and organic managements (Mazzoncini et al., 2010)nd in several systems from monocropping to grasslands in Europend USA (Bever et al., 1996; Oehl et al., 2003; Calvente et al., 2004).uch differences may be due to a low sampling effort in comparisonith the other studies, which is known to affect the observed AMF

ommunity richness (Renker et al., 2006).The presence of the genera Glomus in MW may depend on

he high responsiveness of the Scutellospora genera to tillage,onocropping, fertilisation and pesticide applications (Helgason

t al., 1998; Daniell et al., 2001; Oehl et al., 2004). By contrast, othertudies reported the occurrence of Scutellospora calospora in organicnd low-input agroecosystems based on crop rotation and in con-entional maize monoculture (Oehl et al., 2003, 2004; Mazzoncinit al., 2010). The lower AMF diversity in MW and US than in T1 and2, evaluated here also by H0, is mainly caused by the low numberf spores and would result in low functional contribution to hostsue to AMF functional complementarity (Koide, 2000; Avio et al.,006).

Here, homogenization of the field soil in the sampling enableds to reduce spatial variation that may influence AMF root coloni-ation, infectivity, spore density, community composition andtructure, changing the available pool of AMF (Lekberg et al., 2007;

olfe et al., 2007; Mummey and Rillig, 2008). AMF seasonality haseen studied by several authors in different ecosystems and dates.ost research has revealed temporal dynamics in resting spores in

he soil, which may reflect variation in sporulation rather than inungal presence (Gemma et al., 1989; Schultz et al., 1999). In addi-ion, Helgason et al. (1999), evaluating the AMF diversity withinhe roots of bluebell by morphological and molecular techniques,evealed clear seasonal patterns dependent on fungal species and,hen, Vandenkoornhuyse et al. (2002) found that the AMF commu-ities within Trifolium repens and Agrostis capillaris changed overime, although the authors suggested that a change of management

ay be responsible for this, observing also differences dependentn plant and fungal species. By contrast, the sampling season hado influence on AMF composition and patterns of diversity both inhe field as spores and within the roots as active colonisation (Oehlt al., 2003; Stukenbrock and Rosendahl, 2004).

. Conclusions

This study shows that 10 years after land management change,oil quality under poplar SRC is improved compared with anntensive agricultural cropping system and, unexpectedly, to an

ncultivated system. These aspects have agro-ecological implica-ions, since the positive changes of soil nutrient availability and Content together with a high abundance and diversity of soil biotaeflect low risk of nutrient losses, contribution to climate protectionnd biodiversity, showing a clear soil sustainability of poplar SRC.

nd Environment 140 (2011) 245–254

Differences in soil chemical, biochemical and AMF parameters alsoobserved among the three SRC poplar cutting cycles indicate thatthe choice of a suitable harvest frequency is important to preservesoil fertility and health. Overall, multivariate analysis showed thatT1 and T2 determine changes of parameters related to AMF, exceptfor spore production, while T3 improved chemical and biochemi-cal traits. As mycorrhizal symbiosis establishment and extraradicalmycelium development is dependent on plant fixed C, the potentialreduction of available C following clipping would result in a highmycelium growth from AMF spores and from already colonisedpoplar roots aiming to establish symbiosis with other plant speciesseeking C sources. Our findings of plant–soil biota interactionsunder different SRC harvest intensity may contribute to sustainablebioenergy crop management. Further study on biomass crops isrequired to investigate subsurface layer SOC dynamics and shifts ofsoil microbial community composition, activity and function usingalso molecular techniques.

Acknowledgements

The authors wish to thank the technical staff of the“Enrico Avanzi” Interdepartmental Centre for Agro-EnvironmentalResearch of the University of Pisa, Italy, for their contribution to set-up and management of field experiments. Many thanks also to Prof.Manuela Giovannetti for laboratory facilities, and Dr. Stefano Bedinifor helpful comments on this paper. We thank also three reviewersand the editor for discussions and many constructive comments.

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